Oceans, which cover 70% of the surface of the Earth and form the largest habitat on the planet, face increasing stress as a result of human activities.

Oceans absorb between half and three-quarters of the greenhouse gases that we put into the atmosphere each year. In doing this, the oceans have slowed global warming and climate change.

But,therehasbeenacost.

When carbon dioxide from greenhouse gases dissolves in seawater, it causes the pH level of our oceans to decrease. Seawaterhasbecomemoreacidic(its pH has decreased by 0.1) since the beginning of the industrial era and it will continue to acidify during the 21st century.

Ocean acidification is expected to affect ocean ecosystems, such as coral reefs, and the living organisms that inhabit those ecosystems. It will change ocean life and its food chain – and in turn our fish supplies.

By 2050 it is expected that2outofevery3peoplewillbelivinginurbanareasas growing numbers of people move to cities in search of jobs and opportunities.

Because many cities – includingmegacitieswith populations of more than 10 million – are built along coastlines, they are at exposed to tropical storms. Hurricane Sandy hitting New York in 2012 is an example of the potential damage tropical storms can cause to coastal cities.

Congestion and pollution, and their effects on our health, are other major issues facing urban populations.

Meteorological services have a large role to play due to the influence of weather on:

Energy supplies

Transport systems

Water management

Pollution levels

The WMO urban meteorology programme promotes ways to deal with multiple hazards facing cities while many of WMO Members provide pollution advice to governments who can then turn around and use this information to issue health warnings and traffic restrictions.